There are many useful chemical and biological reactions that take place within a fluid medium. These may be the result of interaction between the fluid medium and the surrounding environment, e.g. oxidation when exposed to air, or they may be a result of mixing the fluid medium with some reagent or another fluid medium containing a reagent. Such chemical and biological reactions may be useful in a variety of areas, such as industrial processing, medical diagnostics, or the like. The use of such chemical and biological reactions often requires suitable measurement equipment, to ascertain whether a particular specified reaction has actually taken place, or further, to provide a measure of the extent of occurrence of the reactions.
There are known methods to measure the existence or extent of reactions within a fluid medium, but they each have associated disadvantages, including speed or accuracy limitations, cost or complexity to carry out, and the like. For example, whilst the binding of specific antibodies and antigens in a fluid medium can be detected using additional tagging techniques, these techniques may change the structure and affinity of binding. Meanwhile, labelling also requires complexity and amplification of weak signals. Label-free methods, where tagging is not used, can be based on methods such as surface plasmon resonance, but these methods lack the ability to carry out multiple parallel tests to allow for measuring several reactions in a hand held device.